Submersible power generator

ABSTRACT

[Object of the Invention] An object of the present invention is to provide a submersible power generator which can be stably moored in water and can generate high electromotive voltage without being increased in size. 
     [Disclosure of the Invention] A submersible power generator comprising relatively rotating inner and outer rotational armatures, propellers for driving the inner and outer rotational armatures to rotate relatively to each other, and a casing for accommodating the inner and outer rotational armatures, which submersible power generator comprises an inner/outer double rotational armatures-type power generation mechanism provided with an outer rotational armature and an inner rotational armature opposing the outer rotational armature to rotate in a direction opposite to a direction of rotation of the outer rotational armature, and a pair of propellers disposed coaxially with blades of one of the pair of propellers and blades of the other of the pair of propellers twisted in opposite directions relative to an extending direction of a central axis of the pair of propellers, wherein one of the propellers is connected to one of the inner and outer rotational armatures and the other of the propellers is connected to the other of the inner and outer rotational armatures, and further comprises a casing for accommodating the inner/outer double rotational armatures-type power generation mechanism and shielding it from an external environment, and which submersible power generator, as installed under water to operate in a water current, is made to have buoyancy F acting thereon which is larger than gravity W acting thereon during operation of the submersible power generator (when the submersible power generator is moored by a mooring wire, F&gt;W+gravity acting on the mooring wire—buoyancy acting on the mooring wire).

TECHNICAL FIELD

The present invention relates to a submersible power generator.

BACKGROUND ART

Patent document No. 1 discloses a submersible power generator comprisingrelatively rotating inner and outer rotational armatures, propellers fordriving the inner and outer rotational armatures to rotate relatively toeach other, and a casing for accommodating the inner and outerrotational armatures, which submersible power generator comprises apower generation mechanism provided with a pair of front and rear outerrotational armatures and a pair of front and rear inner fixed armatures,a pair of front and rear propellers rotating in directions opposite toeach other to rotate the pair of front and rear outer rotationalarmatures in directions opposite to each other, and a casing foraccommodating the pair of front and rear inner fixed armatures andshielding them from an external environment, wherein the submersiblepower generator is installed under water to operate in a water current,and buoyancy acting on the submersible power generator is larger thangravity acting on the submersible power generator.

PRIOR ART DOCUMENTS Patent Documents

Patent Document No. 1: Japanese Patent Laid-Open No. 2007-016786

DISCLOSURE OF INVENTION Problem to be solved

In the aforementioned submersible power generator, the front outerrotational armature driven by the front propeller does not operablyengage the rear outer rotational armature driven by the rear propeller,so that rotational torque impressed on the front inner fixed armature bythe opposing front outer rotational armature and rotational torqueimpressed on the rear inner fixed armature by the opposing rear outerrotational armature are independent of each other kinetically andelectromagnetically during power generation, with the result that thelevels of the two rotational torques do not necessarily become equal toeach other. Therefore, the aforementioned submersible power generatorcannot be stably moored in water.

The electromotive voltage level of the power generation mechanism isproportional to the speed at which the rotational armature cuts amagnetic field. In the submersible power generator, increase of rotationspeed of the propellers should be restrained from the viewpoint ofpreventing occurrence of propeller cavitation. Therefore, in theaforementioned submersible power generator, wherein a pair of sets ofthe outer rotational armature and the opposing inner fixed armature aredisposed independent of each other, it is necessary for generating highelectromotive voltage to provide a speed increasing gear or pulleymechanism for increasing the speed of the rotation of the propellerstransmitted to the outer rotational armatures. Provision of a speedincreasing gear or pulley mechanism increases the size of the powergenerator.

Therefore, an object of the present invention is to provide asubmersible power generator which can be stably moored in water and cangenerate high electromotive voltage without being increased in size.

Means for Achieving the Object

In accordance with the present invention, there is provided asubmersible power generator comprising relatively rotating inner andouter rotational armatures, propellers for driving the inner and outerrotational armatures to rotate relatively to each other, and a casingfor accommodating the inner and outer rotational armatures, whichsubmersible power generator comprises an inner/outer double rotationalarmatures-type power generation mechanism provided with an outerrotational armature and an inner rotational armature opposing the outerrotational armature to rotate in a direction opposite to a direction ofrotation of the outer rotational armature, and a pair of propellersdisposed coaxially with blades of one of the pair of propellers andblades of the other of the pair of propellers twisted in oppositedirections relative to an extending direction of a central axis of thepair of propellers, wherein one of the propellers is connected to one ofthe inner and outer rotational armatures and the other of the propellersis connected to the other of the inner and outer rotational armatures,and further comprises a casing for accommodating the inner/outer doublerotational armatures-type power generation mechanism and shielding itfrom an external environment, and which submersible power generator, asinstalled under water to operate in a water current, is made to havebuoyancy F acting thereon which is larger than gravity W acting thereonduring operation of the submersible power generator (when thesubmersible power generator is moored by a mooring wire, F>W+gravityacting on the mooring wire—buoyancy acting on the mooring wire).

In the submersible power generator in accordance with the presentinvention, reciprocal rotational torques acting on the inner/outerdouble rotational armatures during power generation become equal to eachother kinetically and electromagnetically according to the third law ofmotion (action-reaction law), so that reciprocal rotational torquesacting on an inner rotary system formed by the inner rotational armatureand the propeller connected to the inner rotational armature and anouter rotary system formed by the outer rotational armature and thepropeller connected to the outer rotational armature become equal andcancel each other. As a result, no reactionary rotational torque isimpressed on the casing. Therefore, the submersible power generator inaccordance with the present invention can be stably moored in waterwithout incurring rotation of the casing around the central axis of thepropellers, irrespective of power generation amount and water currentspeed.

In the submersible power generator in accordance with the presentinvention, the pair of propellers, which are disposed coaxially withblades of one of the pair of propellers and blades of the other of thepair of propellers twisted in opposite directions relative to anextending direction of a central axis of the pair of propellers, rotatein opposite directions to rotate the inner/outer rotational armatures indirections opposite to each other. Therefore, relative rotation speedbetween the inner/outer rotational armatures can be increased, withincrease of rotation speed of the propellers restricted, so as toincrease the speed at which the inner/outer rotational armatures cut amagnetic field. As a result, electromotive voltage higher than thatobtained by the conventional submersible power generator can be obtainedwithout causing an increase in size due to provision of a speedincreasing gear or pulley mechanism. On the other hand, whenelectromotive voltage is set at the same level as that of theconventional submersible power generator, the number of windings of thearmatures can be decreased, a permanent magnet forming the armature of asynchronous generator can be downsized, and the rotation radius of thearmature can be decreased, so that the submersible power generator inaccordance with the present invention can be made smaller than theconventional submersible power generator because the speed at which theinner/outer rotational armatures of the submersible power generator ofthe present invention cut a magnetic field is higher than the speed atwhich the rotational armatures of the conventional submersible powergenerator cut a magnetic field.

Buoyancy F acting on the submersible power generator is larger thangravity W acting thereon during operation of the submersible powergenerator (when the submersible power generator is moored by a mooringwire, F>W+gravity acting on the mooring wire—buoyancy acting on themooring wire). Therefore, the submersible power generator in accordancewith the present invention can be easily and stably moored by a mooringwire, etc., without being provided with an additional float member.

In accordance with a preferred aspect of the present invention, polarmoment of inertia of one of the pair of propellers is set at a levellower than polar moment of inertia of the other of the pair ofpropellers.

When polar moment of inertia of one of the pair of propellers is set ata level lower than polar moment of inertia of the other of the pair ofpropellers, start of said one of the pair of propellers in a watercurrent can be advanced so as to advance start of the power generator.

In accordance with a preferred aspect of the present invention, as seenon a meridian plane (a vertical plane including a rotational axis of thepropellers), a rotational moment center, around which a sum total ofrotational moments generated by the buoyancy F acting on the submersiblepower generator, the gravity W acting on the submersible power generatorand drag D acting on the submersible power generator in a water currentbecomes zero, comes to be located on the casing.

When a rotational moment center assumes a location on the casing as seenon a meridian plane, the submersible power generator can be stably heldin water by some means on an axis passing through the rotational momentcenter and crossing the meridian plane at right angles.

In accordance with a preferred aspect of the present invention, therotational moment center is located on an action line of the drag Dacting on the submersible power generator, and the submersible powergenerator is supported rotatably around an axis passing through therotational moment center and crossing the meridian plane at rightangles.

The aforementioned manner of support makes it possible to horizontallyhold the submersible power generator irrespective of water currentspeed.

In accordance with the present invention, there is provided asubmersible power generation system comprising the aforementionedsubmersible power generator as moored in a water current by a mooringwire connected to the casing rotatably around an axis passing throughthe rotational moment center and crossing the meridian plane at rightangles.

In a submersible power generation system in accordance with the presentinvention, the submersible power generator can be stably held also asseen on the meridian plane irrespective of power generation amount andwater current speed because the submersible power generator is moored ina water current by a mooring wire connected to the casing rotatablyaround an axis passing through the rotational moment center and crossingthe meridian plane at right angles.

In accordance with a preferred aspect of the present invention, one ormore mooring wires are connected to the casing symmetrically bilaterallyrelative to the action line of the drag D as seen along the extendingdirection of the action line of the drag D.

The aforementioned manner of support makes it possible to prevent yawingof the submersible power generator caused by the drag D and stably holdthe submersible power generator in water.

In accordance with a preferred aspect of the present invention, afork-shaped arm member is connected to the casing rotatably around anaxis passing through the rotational moment center and crossing themeridian plane at right angles, and a mooring wire is connected to thearm member rotatably or pivotably relative to the arm member.

When a fork-shaped arm member is connected to the casing rotatablyaround an axis passing through the rotational moment center and crossingthe meridian plane at right angles, and a mooring wire is connected tothe arm member rotatably or pivotably relative to the arm member, itbecomes possible to stably hold the power generator in water even by asingle mooring wire.

In accordance with a preferred aspect of the present invention, one ormore mooring wires are connected to the casing symmetrically bilaterallyrelative to the action line of the drag D as seen along the extendingdirection of the action line of the drag D.

The aforesaid manner of support makes it possible to prevent yawing ofthe submersible power generator caused by the drag D and stably hold thesubmersible power generator in water.

In accordance with a preferred aspect of the present invention, thecasing is provided with a stopper for restricting swing motion of a freeend of the fork-shaped member toward the propellers.

When the casing is provided with a stopper for restricting swing motionof a free end of the fork-shaped member toward the propellers, the oneor more mooring wires attached to the free end of the fork-shaped memberare prevented from interfering with the propellers.

In accordance with a preferred aspect of the present invention, anaction line of the buoyancy F acting on the submersible power generatorbecomes located upstream of an action line of the gravity W acting onthe submersible power generator.

When the action line of the buoyancy F is located upstream of the actionline of the gravity W, the rotational moment center becomes locatedupstream of the action line of the buoyancy F, so that the mooring wireor the mooring wires are distanced from the propellers and interferenceof the mooring wire or the mooring wires with the propellers is moreeffectively prevented.

In accordance with the present invention, there is provided asubmersible power generation system comprising the aforementionedsubmersible power generator as supported on an axis passing through therotational moment center and crossing the meridian plane at right anglesby a support fixed to a seabed or a riverbed and extending upward.

In accordance with the present invention, there is provided asubmersible power generation system comprising the aforementionedsubmersible power generator as supported on an axis passing through therotational moment center and crossing the meridian plane at right anglesby a support extending downward from a float on a water surface.

In the aforementioned submersible power generation system, no force isimpressed on the support from the submersible power generator other thanan upward force owing to difference between the buoyancy F and thegravity W of the submersible power generator and the drag crossing theupward force at right angles, so that a coupling portion between thesupport and the submersible power generator becomes simple in structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of a submersible power generator inaccordance with a preferred embodiment of the present invention.

FIG. 2 is a side view of a submersible power generator in accordancewith a preferred embodiment of the present invention showing arotational moment center, around which a sum total of rotational momentsgenerated by the buoyancy F acting on the submersible power generator,the gravity W acting on the submersible power generator and drag Dacting on the submersible power generator in a water current becomeszero.

FIG. 3 is a side view of a submersible power generation systemcomprising a submersible power generator in accordance with a preferredembodiment of the present invention.

FIG. 4 is a front view of a variation of the submersible powergeneration system comprising a submersible power generator in accordancewith a preferred embodiment of the present invention.

FIG. 5 is a front view of another variation of the submersible powergeneration system comprising a submersible power generator in accordancewith a preferred embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

A submersible power generator and a submersible power generation systemin accordance with preferred embodiments of the present invention willbe described.

As shown in FIG. 1, a submersible power generator A comprises aninner/outer double rotational armatures-type power generation mechanism3 provided with a cylindrical outer shaft 1 a, an inner shaft 1 bcoaxially passing through the outer shaft 1 a, an outer rotationalarmature 2 a fixed to the outer shaft 1 a and an inner rotationalarmature 2 b fixed to the inner shaft 1 b and opposing the outerrotational armature 2 a, a front propeller 4 a fixed to the outer shaft1 a so as to rotate the outer shaft 1 a and the outer rotationalarmature 2 a, a rear propeller 4 b located rearward of the frontpropeller 4 a relative to a direction of water current indicated by ablank arrow in FIG. 1, disposed coaxially and in alignment with thefront propeller 4 a, and fixed to the inner shaft 1 b so as to rotatethe inner shaft 1 b and the inner rotational armature 2 b, and abombshell shaped casing 5 for accommodating the inner/outer doublerotational armatures-type power generation mechanism 3 and shielding itfrom an external environment. A twisting direction of blades of thefront propeller 4 a and a twisting direction of blades of the rearpropeller 4 b relative to an extending direction of a central axis ofthe propellers 4 a and 4 b are opposite to each other. A polar moment ofinertia of the rear propeller 4 b is set at a level lower than a polarmoment of inertia of the front propeller 4 a.

Shape, size and weight of the structural members of the submersiblepower generator A are designed so that a formula F>W (when thesubmersible power generator is moored by a mooring wire, F>W+gravityacting on the mooring wire—buoyancy acting on the mooring wire) isestablished, wherein F is buoyancy acting on the submersible powergenerator A when the submersible power generator A is located in a watercurrent as indicated by a blank arrow in FIG. 2, W is gravity acting onthe submersible power generator A, and D is drag acting on thesubmersible power generator A. Further, the shape, size and weight ofthe structural members of the submersible power generator A are designedso that, as seen on a meridian plane (a vertical plane including arotational axis of the propellers), a rotational moment center, aroundwhich a sum total of rotational moments generated by the buoyancy Facting on the submersible power generator and directed verticallyupward, the gravity W acting on the submersible power generator anddirected vertically downward and drag D acting on the submersible powergenerator and directed in parallel with the water current becomes zero,comes to be located on the casing 5. When the aforementioned forces F, Wand D are indicated by vectors (action lines) passing through workingpoints as shown in FIG. 2, distances between a center of the frontpropeller 4 a to the vectors F and W are indicated by SF and Sw, and arotational moment center is located on the action line of the drag D,and a distance S from the center of the front propeller 4 a to therotational moment center C measured in an extending direction of thecentral axis of the propeller 4 a is indicated by a formula:

S=(F·S _(F) −W·S _(W))/(F−W)

The location of the rotational moment center C does not move even asseen on a plane parallel to the meridian plane.

As shown in FIG. 3, the casing 5 of the submersible power generator A isconnected to a fork-shaped arm member 6 of a bilaterally symmetricalshape as seen along the central axis of the propellers at opposite sideportions. The fork-shaped member 6 is connected to the casing 5rotatably around an axis C′ passing through the rotational moment centerC and crossing the meridian plane at right angles. As can be seen fromFIG. 3( b), one end of a mooring wire 8 is connected to a free end ofthe fork-shaped member 6 through a slip ring 7 rotatably relative to thefork-shaped member 6 and symmetrically bilaterally relative to theaction line of the drag D as seen in the extending direction of theaction line of the drag D, and the other end of the mooring wire 8 isconnected to an anchor 9 such as a tetrapod or the like installed in aseabed or riverbed 100. Thus, the submersible power generator A ishorizontally moored in a water current with the propellers 4 a and 4 bautomatically directed to the downstream side of the water currentindicated by a blank arrow in FIG. 3 and accordingly the bombshell headshaped end portion of the casing 5 distanced from the propellers 4 a and4 b directed to the upstream side of the water current. The submersiblepower generator A and aforementioned mooring members form a submersiblepower generation system B.

The mooring wire 8 of the submersible power generation system B forms acatenary as seen on the meridian plane, which is determined by theaforementioned buoyancy F, gravity G, drag D, buoyancy acting on themooring wire 8, and gravity acting on the mooring wire 8. Curvature ofthe catenary becomes smaller as water current speed becomes slower. Whenwater current speed becomes zero, the mooring wire 8 extends verticallyfrom the anchor 9. Therefore, the mooring wire 8 does not interfere withthe propellers 4 a and 4 b irrespective of fluctuation of the speed anddirection of the water current.

Operations of the submersible power generator A and the submersiblepower generation system B will be described.

As the twisting directions of the blades of the front and rearpropellers 4 a and 4 b relative to the extending direction of thecentral axis of the propellers 4 a and 4 b are opposite to each other,the front and rear propellers 4 a and 4 b rotate in opposite directionsin the water current as indicated by a blank arrow in FIG. 3. Thepropellers 4 a and 4 b drive the outer/inner rotational armatures 2 aand 2 b through outer/inner shafts 1 a and 1 b to rotate them indirections opposite to each other, thereby generating electric power.Generated electric power is taken out of the power generator through thearm member 6, the slip ring 7, the mooring wire 8 and a cable integrallyunited with the mooring wire 8, and supplied to land electric equipmentthrough cables laid over the bottom of the water body or supplied toelectric equipment on the water through cables elevated above the water.

In the submersible power generator A, reciprocal rotational torquesacting on the inner/outer double rotational armatures 2 a and 2 b duringpower generation become equal to each other, and reciprocal rotationaltorques acting on an inner rotary system formed by the inner rotationalarmature 2 b, the inner shaft 1 b and the rear propeller 4 b connectedto the inner rotational armature 2 b and an outer rotary system formedby the outer rotational armature 2 a, the outer shaft 1 a and the frontpropeller 4 a connected to the outer rotational armature 2 a becomeequal to each other kinetically and electromagnetically in accordancewith the third law of motion so as to cancel each other. As a result, noreactionary rotational torque is impressed on the casing 5. Therefore,the submersible power generator A can be stably moored in water withoutincurring rotation of the casing 5 around the central axis of propellersirrespective of fluctuation of power generation amount and water currentspeed.

In the submersible power generator A, the power generation mechanism 3comprises the outer rotational armature 2 a and the inner rotationalarmature 2 b rotating in the direction opposite to the rotationaldirection of the outer rotational armature 2 a, and the pair offront/rear double propellers 4 a and 4 b rotating in directions oppositeto each other rotate the inner/outer rotational armatures 2 a and 2 bopposing each other in directions opposite to each other. Therefore,relative rotation speed between the inner/outer rotational armatures 2 aand 2 b can be increased so as to increase the speed at which theinner/outer rotational armatures cut a magnetic field, while restrainingincrease of rotation speeds of the propellers 4 a and 4 b. As a result,electromotive voltage higher than that obtained by the conventionalsubmersible power generator can be obtained without increase of size dueto provision of a speed increasing gear or pulley mechanism. On theother hand, when electromotive voltage is set at the same level as thatof the conventional submersible power generator, the number of windingsof the armatures 2 a and 2 b can be decreased, a permanent magnetforming the armature of a synchronous generator can be downsized, androtation radius of the armature can be decreased, so that thesubmersible power generator A can be made smaller than the conventionalsubmersible power generator because the speed at which the inner/outerrotational armatures 2 a and 2 b cut a magnetic field is larger than thespeed at which the rotational armatures of the conventional submersiblepower generator cut a magnetic field.

The buoyancy F acting on the submersible power generator A is largerthan the gravity W acting on the submersible power generator A duringoperation of the submersible power generator A (when the submersiblepower generator A is moored by a mooring wire, F>W+gravity acting on themooring wire—buoyancy acting on the mooring wire). Therefore, thesubmersible power generator A can be easily and stably held in the waterwithout being provided with an additional float member.

Polar moment of inertia of the rear propeller 4 b is set at a levellower than polar moment of inertia of the front propeller 4 a, so thatstart of the rear propeller 4 b in a water current is advanced so as toadvance start of the power generator A.

In the submersible power generator A, as seen on the meridian plane, therotational moment center, around which the sum total of rotationalmoments generated by the buoyancy F acting on the submersible powergenerator A, the gravity W acting on the submersible power generator Aand drag D acting on the submersible power generator A in a watercurrent becomes zero, comes to be located on the casing 5. Therefore,the submersible power generator A can be stably held in water also onthe meridian plane by some means on an axis passing through therotational moment center and crossing the meridian plane at rightangles.

In the submersible power generation system B, the rotational momentcenter is located on the action line of the drag D, and the casing 5 issupported at both sides rotatably around an axis C′ passing through therotational moment center C and crossing the meridian plane at rightangles. The aforementioned manner of support makes it possible tohorizontally hold the submersible power generator A irrespective ofwater current speed.

In the submersible power generation system B, the submersible powergenerator A can be stably held irrespective of power generation amountand water current speed because the submersible power generator A ismoored in water by the mooring wire 8 connected to the casing 5rotatably around the axis C′ passing through the rotational momentcenter C and crossing the meridian plane at right angles. The wire 8 isconnected to the casing 5 symmetrically bilaterally relative to theaction line of the drag D as seen along the extending direction of theaction line of the drag D. The aforesaid manner of support makes itpossible to prevent yawing of the submersible power generator A causedby the drag D and stably hold the submersible power generator A inwater.

In the submersible power generation system B, the fork-shaped arm member6 is connected to the casing 5 rotatably around the axis C′ passingthrough the rotational moment center C and crossing the meridian planeat right angles, and the mooring wire 8 is connected to the arm member 6through a slip ring 7 capable of rotation relative to the arm member 6and symmetrically bilaterally relative to the action line of the drag Das seen along the extending direction of the action line of the drag D.The aforementioned manner of support makes it possible to stably holdthe submersible power generator A in water by a single mooring wire 8irrespective of power generation amount and water current speed.

The present invention is not restricted to the aforementioned preferredembodiment.

The submersible power generator A can be moored in water by a pair ofmooring wires 8 connected to the opposite side portions of the casing 5rotatably around the axis C′ passing through the rotational momentcenter C and crossing the meridian plane at right angles andsymmetrically bilaterally relative to the action line of the drag D asseen along the extending direction of the action line of the drag D.

The mooring wire 8 can be connected to the arm member 6 pivotablythrough a universal joint.

A plurality of mooring wires 8 can be connected to the arm member 6. Inthis case, the mooring wires 8 are desirably connected to the arm member6 symmetrically bilaterally relative to the action line of the drag D asseen along the extending direction of the action line of the drag D.

As indicated by dashed-dotted lines in FIG. 3, the casing 5 can beprovided with a stopper 10 for restricting swing motion of a free end ofthe fork-shaped arm member 6 toward the propellers 4 a and 4 b.

When the swing motion of a free end of the fork-shaped arm member 6toward the propellers 4 a and 4 b is restricted within an appropriaterange, the mooring wire 8 attached to the free end of the fork-shapedarm member 6 is easily prevented from interfering with the propellers 4a and 4 b.

When the action line of the buoyancy F is located upstream of the actionline of the gravity W as shown in FIG. 2, the rotational moment center Cbecomes located upstream of the action line of the buoyancy F, so thatthe mooring wire 8 is distanced from the propellers 4 a and 4 b andinterference of the mooring wire 8 with the propellers 4 a and 4 b iseffectively prevented irrespective of water current speed.

It is possible as shown in FIG. 4 to connect the fork-shaped arm member6′ to the casing 5 rotatably around the axis C′ passing through therotational moment center C and crossing the meridian plane at rightangles, and support a base portion of the arm member 6′ rotably around avertical axis by a support 11 fixed to a seabed or a riverbed 100 andextending upward. It is possible as shown in FIG. 5 to connect thefork-shaped arm member 6′ to the casing 5 rotatably around the axis C′passing through the rotational moment center C and crossing the meridianplane at right angles, and support a base portion of the arm member 6′rotably around a vertical axis by a support 11 extending downward from afloat 200 on the water surface. In the aforementioned submersible powergeneration systems, no force is impressed on the support 11 from thesubmersible power generator A other than an upward force owing todifference between the buoyancy F and the gravity W of the submersiblepower generator A and the drag D crossing the difference upward force atright angles, so that the structure of a coupling portion between thesupport 11 and the submersible power generator A becomes simple. Thefloat 200 can be easily moored.

When the base portion of the arm member 6′ is supported rotatably arounda vertical axis, the submersible power generator A can be laid along thewater current.

When the support 11 is made telescopic, the submersible power generatorA can be located at an optimum water depth position. IndustrialApplicability

The present invention can be widely used for submersible powergenerators and submersible power generation systems irrespective ofwhether offshore installation type or river installation type.

BRIEF DESCRIPTION OF THE REFERENCE NUMERALS

A Submersible power generator

B Submersible power generation system

1 a Outer shaft

1 b Inner shaft

2 a Outer rotational armature

2 b Inner rotational armature

3 Power generation mechanism

4 a Front propeller

4 b Rear propeller

5 Casing

6, 6′ Arm member

7 Slip ring

8 Mooring wire

9 Anchor

10 Stopper

11 Support

100 Seabed or riverbed

200 Float

1. A submersible power generator comprising relatively rotating innerand outer rotational armatures, propellers for driving the inner andouter rotational armatures to rotate relatively to each other, and acasing for accommodating the inner and outer rotational armatures, whichsubmersible power generator comprises an inner/outer double rotationalarmatures-type power generation mechanism provided with an outerrotational armature and an inner rotational armature opposing the outerrotational armature to rotate in a direction opposite to a direction ofrotation of the outer rotational armature, and a pair of propellersdisposed coaxially with blades of one of the pair of propellers andblades of the other of the pair of propellers twisted in oppositedirections relative to an extending direction of a central axis of thepair of propellers, wherein one of the propellers is connected to one ofthe inner and outer rotational armatures and the other of the propellersis connected to the other of the inner and outer rotational armatures,and further comprises a casing for accommodating the inner/outer doublerotational armatures-type power generation mechanism and shielding itfrom an external environment, and which submersible power generator, asinstalled under water to operate in a water current, is made to havebuoyancy F acting thereon which is larger than gravity W acting thereonduring operation of the submersible power generator (when thesubmersible power generator is moored by a mooring wire, F>W+gravityacting on the mooring wire—buoyancy acting on the mooring wire).
 2. Asubmersible power generator of claim 1, wherein polar moment of inertiaof one of the pair of propellers is set at a level lower than polarmoment of inertia of the other of the pair of propellers.
 3. Asubmersible power generator of claim 1, wherein, as seen on a meridianplane (a vertical plane including a rotational axis of the propellers),a rotational moment center, around which a sum total of rotationalmoments generated by buoyancy F acting on the submersible powergenerator, gravity W acting on the submersible power generator and dragD acting on the submersible power generator in a water current becomeszero, comes to be located on the casing.
 4. A submersible powergenerator of claim 3, wherein the rotational moment center is located onan action line of the drag D acting on the submersible power generator,and the submersible power generator is supported rotatably around anaxis passing through the rotational moment center and crossing themeridian plane at right angles.
 5. A submersible power generationsystem, comprising the submersible power generator of claim 3 as mooredin water by a mooring wire connected to the casing rotatably around anaxis passing through the rotational moment center and crossing themeridian plane at right angles.
 6. A submersible power generation systemof claim 5, wherein one or more mooring wires are connected to thecasing symmetrically bilaterally relative to the action line of the dragD as seen along the extending direction of the action line of the dragD.
 7. A submersible power generation system of claim 5, wherein afork-shaped arm member is connected to the casing rotatably around anaxis passing through the rotational moment center and crossing themeridian plane at right angles, and the mooring wire is connected to thearm member rotatably or pivotably relative to the arm member.
 8. Asubmersible power generation system of claim 7, wherein one or moremooring wires are connected to the arm member symmetrically bilaterallyrelative to the action line of the drag D as seen along the extendingdirection of the action line of the drag D.
 9. A submersible powergeneration system of claim
 7. wherein the casing is provided with astopper for restricting swing motion of a free end of the fork-shapedarm member toward the propellers.
 10. A submersible power generationsystem of claim 5, wherein an action line of the buoyancy F acting onthe submersible power generator becomes located upstream of an actionline of the gravity W acting on the submersible power generator.
 11. Asubmersible power generation system, comprising the submersible powergenerator of claim 3 as supported on an axis passing through therotational moment center and crossing the meridian plane at right anglesby a support fixed to a seabed or a riverbed and extending upward.
 12. Asubmersible power generation system, comprising the submersible powergenerator of claim 3 as supported on an axis passing through therotational moment center and crossing the meridian plane at right anglesby a support extending downward from a float on a water surface.
 13. Asubmersible power generation system, comprising the submersible powergenerator of claim 4 as moored in water by a mooring wire connected tothe casing rotatably around an axis passing through the rotationalmoment center and crossing the meridian plane at right angles.
 14. Asubmersible power generation system of claim 13, wherein one or moremooring wires are connected to the casing symmetrically bilaterallyrelative to the action line of the drag D as seen along the extendingdirection of the action line of the drag D.
 15. A submersible powergeneration system of claim 13, wherein a fork-shaped arm member isconnected to the casing rotatably around an axis passing through therotational moment center and crossing the meridian plane at rightangles, and the mooring wire is connected to the arm member rotatably orpivotably relative to the arm member.
 16. A submersible power generationsystem of claim 15, wherein one or more mooring wires are connected tothe arm member symmetrically bilaterally relative to the action line ofthe drag D as seen along the extending direction of the action line ofthe drag D.
 17. A submersible power generation system of claim 15wherein the casing is provided with a stopper for restricting swingmotion of a free end of the fork-shaped arm member toward thepropellers.
 18. A submersible power generation system of claim 13,wherein an action line of the buoyancy F acting on the submersible powergenerator becomes located upstream of an action line of the gravity Wacting on the submersible power generator.
 19. A submersible powergeneration system, comprising the submersible power generator of claim 4as supported on an axis passing through the rotational moment center andcrossing the meridian plane at right angles by a support fixed to aseabed or a riverbed and extending upward.
 20. A submersible powergeneration system, comprising the submersible power generator of claim 4as supported on an axis passing through the rotational moment center andcrossing the meridian plane at right angles by a support extendingdownward from a float on a water surface.